if you had bad posture (both when walking / working) and you permanently fixed it, reply what you did, what content you followed, what habits you had if you did not fix or never had bad posture but give advice, make a disclaimer

my only insight so far personally is that it has all to do with ONE muscle, the one you can push out your chest with. if i constantly push my chest out everything else just aligns perfectly, but how df do i work out that muscle? i tried deadlife, rows, hyper extension etc